Using Nano-Scale Mechanical Property Characterization to Explore the Impact of Molecular Composition on Power Conversion Efficiency in Polymer/Fullerene Bulk-Heterojunction Solar Cell
| Autor: | Hung-Chang Li, 李鴻昌 |
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| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 Recently the organic hetero-junction solar cell has attracted much research interest due to their advantages of easy fabrications and large, flexible area. Most of these investigation focus on the solar cells with active layers composed P3HT/PCBM (poly[3-hexylthiophene] / [6,6]-phenyl-C61-butyric acid methyl ester) for electron donor and acceptor to increase the power conversion efficiency (PCE). These researches indicate that different fabrication conditions and blended proportion would affect the PCE and surface morphology of a active layer (P3HT: PCBM). However, the characterization of morphology remains a hurdle. Therefore the understanding of structure morphology of active layer on hetero-junction solar cells PCE is lacking. This study utilizes the nano-indentation technique to explore the relationship among the composition structure, PCE and local mechanical property. It is expected that this relationship can provide the insight of how structure morphology affects the PCE. This study fabricates the hetero-junction solar cells under different annealed temperature, annealed time, film growth rate, and blended proportion. The solar cell performance tests are conducted by simulating the sunlight at A.M. 1.5G, 100mW/cm2. The optimum PCE can be obtained with annealed temperature of 110 ℃, annealed time of 10 minute, slow growth, and blended proportion 1:1. Under the optimum PCE condition, the measurement of atomic force microscopy (AFM) show pronounced surface height distribution and obvious micro phase separation. The measurements of nano-indentation further reveal the lowest mechanical properties under optimum PCE. These results indicate that micro phase separation exists not only on the surface but also for the entire composition structure when PCE occures. Therefore, it can be postulated that a regular arrangement of inter-chain spacing and self-organization of P3HT with proper PCBM cluster can lead to micro phase separation and profound active layer surface height variation that provide suitable paths for electron-hop and hole-transfer enhancement. In turn, this kind of polymer composition structure will result in weak local mechanical property. This proposed mechanism provides insight for the future study on better power conversion efficiency of organic hetero-junction solar cells. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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